A gas turbine engine generally includes a fan and a core arranged in flow communication with one another. Additionally, the core of the gas turbine engine generally includes, in serial flow order, a compressor section, a combustion section, a turbine section, and an exhaust section. In operation, air is provided from the fan to an inlet of the compressor section where one or more axial compressors progressively compress the air until it reaches the combustion section. Fuel is mixed with the compressed air and burned within the combustion section to provide combustion gases. The combustion gases are routed from the combustion section to the turbine section. The flow of combustion gases through the turbine section drives the turbine section and is then routed through the exhaust section, e.g., to atmosphere.
In general, turbine performance and efficiency may be improved by increased combustion gas temperatures. However, increased combustion temperatures can negatively impact the gas turbine engine components, for example, by increasing the likelihood of material failures. More commonly, non-traditional high temperature materials, such as ceramic matrix composite (CMC) materials, are being used for various components within gas turbine engines. Because CMC materials can withstand relatively extreme temperatures, there is particular interest in replacing components within the flow path of the combustion gases with CMC components, i.e., components formed from CMC materials. Thus, turbine performance and efficiency can be improved through the use of CMC components.
Examples of CMC materials, and particularly SiC/Si-SiC (fiber/matrix) continuous fiber-reinforced ceramic composite (CFCC) materials and processes, are disclosed in U.S. Pat. Nos. 5,015,540; 5,330,854; 5,336,350; 5,628,938; 6,024,898; 6,258,737; 6,403,158; and 6,503,441, and U.S. Patent Application Publication No. 2004/0067316. Such processes generally entail the fabrication of CMCs using multiple pre-impregnated (prepreg) layers, each in the form of a “tape” comprising the desired ceramic fiber reinforcement material, one or more precursors of the CMC matrix material, and organic resin binders. According to conventional practice, prepreg tapes can be formed by impregnating the reinforcement material with a slurry that contains the ceramic precursor(s) and binders. Preferred materials for the precursor will depend on the particular composition desired for the ceramic matrix of the CMC component, for example, SiC powder and/or one or more carbon-containing materials if the desired matrix material is SiC. Notable carbon-containing materials include carbon black, phenolic resins, and furanic resins, including furfuryl alcohol (C4H3OCH2OH). Other typical slurry ingredients include organic binders (for example, polyvinyl butyral (PVB)) that promote the flexibility of prepreg tapes, and solvents for the binders (for example, toluene and/or methyl isobutyl ketone (MIBK)) that promote the fluidity of the slurry to enable impregnation of the fiber reinforcement material. The slurry may further contain one or more particulate fillers intended to be present in the ceramic matrix of the CMC component, for example, silicon and/or SiC powders in the case of a Si-SiC matrix. The resulting prepreg tape may be laid-up with other tapes, and then debulked and, if appropriate, cured while subjected to elevated pressures and temperatures to produce a preform. The preform is then heated (fired) in a vacuum or inert atmosphere to decompose the binders, remove the solvents, and convert the precursor to the desired ceramic matrix material. Due to decomposition of the binders, the result is a porous CMC body that may undergo densification, e.g., melt infiltration (MI), to fill the porosity and yield the CMC component. Specific processing techniques and parameters for the above process will depend on the particular composition of the materials.
Conventional slurries often require solvents in amounts of about 50 weight percent or more to yield tapes that are workable as a result of containing a sufficient amount of solvent, e.g., about 10 to about 20 weight percent solvent. However, typical solvents, including toluene and MIBK, are toxic and flammable, necessitating careful processing, handling, and shipping of the slurries and tapes. In addition, burn-off of typical solvents during firing of the preform results in dimensional changes that interfere with the ability to produce CMC components of consistent dimensions. Moreover, plies produced from tapes using conventional slurries typically are laid up manually, i.e., by hand, and such layups are prone to out-of-alignment plies and ergonomic issues for the assembler. Additionally, manual layups usually result in a large degree of bulk, which can lead to gaps between plies that reduce the material properties of the resulting component.
U.S. Patent Application Publication No. 2013/0157037 describes compositions and processes for producing composite articles, and more specifically, slurry and prepreg tape compositions that are safer to process, handle, and transport, as well as capable of achieving greater dimensional consistency during processing to produce composite articles. In particular, the slurry composition contains particles of a precursor that converts to a ceramic material when heated to a firing temperature, at least one binder that is capable of adhering the particles of the ceramic precursor together to form a flexible prepreg tape, at least one liquid plasticizer, and a solvent in which the binder is dissolved. The solvent is sufficiently volatile to evaporate from the slurry composition during forming of the tape so that the tape contains less than ten weight percent of the solvent, yet the tape is also flexible as a result of the slurry composition containing a sufficient amount of the liquid plasticizer. Using slurry and prepreg tape compositions such as those described in U.S. Pub. No. 2013/0157037, CMC plies may be produced that contain, in addition to the ceramic fibers in the tow and solid particulates in the matrix that will become part of the final material, minimal to no solvents and a binder system that is substantially dry at room temperature but tacky and adhesive at elevated temperatures. Because the tackiness and adhesiveness is reduced or disappears at lower temperatures, manipulation of such dried plies can be automated. Automation of ply layup can reduce or eliminate misaligned plies, eliminate ergonomic issues related to manual layup, and reduce bulk during layup.
Therefore, improved methods for forming ceramic matrix composite components would be desirable. In particular, an automated method of laying up CMC plies would be beneficial. Moreover, a method for forming CMC components using dried pre-impregnated tapes would be desirable. Further, a method for forming CMC components including mechanically transferring and/or positioning plies during ply layup would be advantageous. Additionally, a CMC component formed from an automated ply layup process would be useful.